Prolonged second stage of labor beyond historical definitions is associated with high rates of successful vaginal birth but increased risks of maternal and neonatal morbidity.1 Specifically, prolonging the second stage of labor is associated with increased maternal morbidity including postpartum hemorrhage, maternal febrile morbidity, infection, and perineal trauma. There is also increased neonatal morbidity including increased rates of 5-minute Apgar score less than 4 (except nulliparous women without an epidural), neonatal intensive care unit (NICU) admission, neonatal asphyxia in nulliparous women, and perinatal mortality for deliveries without an epidural; however, the overall absolute rates for both of these latter outcomes are low (less than 0.5%).1
In a workshop including the Society for Maternal-Fetal Medicine and the American College of Obstetricians and Gynecologists to prevent the first cesarean delivery, it was recommended that second-stage arrest could be defined after an additional hour: 4 and 3 hours for nulliparous women with and without an epidural, respectively, and 3 and 2 hours for multiparous women with and without an epidural, respectively.2 Clinical counseling and decision-making require weighing the likelihood of achieving vaginal birth with the risks of complications that can occur with increasing second-stage duration. Information on the risks of specific durations for second stage of labor is currently lacking.3,4 The aim of our study was to calculate the likelihood of vaginal birth without serious maternal or neonatal morbidity or mortality compared with birth with morbidity or mortality to assist in clinical decision-making.
MATERIALS AND METHODS
This was a retrospective analysis using the data from the Consortium on Safe Labor. The Consortium on Safe Labor was a retrospective study of electronic medical records from 12 U.S. sites, 2002–2008, with a main study aim of determining the optimal time for operative birth during the course of labor to minimize maternal and neonatal complications.5 Data were abstracted from the electronic medical record including demographic, medical, prenatal, antenatal, and labor and birth and neonatal information, and supplemented with maternal and newborn discharge summaries. Validation of four important variables was performed with manual chart review, including cesarean delivery for nonreassuring fetal heart rate tracing, asphyxia, NICU admission for respiratory conditions, and shoulder dystocia. The electronic medical records were demonstrated to be highly accurate with greater than 91% concordance for all subgroups and greater than 95% for most.5 Institutional review board approval was obtained by all participating institutions.
In the current study analysis, we included all women who delivered a singleton, vertex, nonanomalous neonate at 36 weeks of gestation or greater. Women who had an antepartum stillbirth, prior uterine incision, or failed to reach the second stage of labor were excluded for a total of n=43,810 nulliparous and 59,605 multiparous women remaining for the present analysis. Details on the analytic cohort were previously published.1
Duration of the second stage of labor was calculated as the difference between the date and time of birth from the date and time of 10-cm cervical dilation as recorded in the maternal medical record. Spontaneous vaginal birth was chosen as the reference group because operative vaginal and cesarean deliveries are associated with increased maternal and neonatal morbidity.
When considering what would be the optimal duration of the second stage of labor, we considered any serious maternal or neonatal outcome as an event to be avoided. Therefore, an event was considered to have occurred if any of the outcomes were present. Maternal and neonatal outcomes were abstracted from the medical record. Composite maternal serious complications included postpartum hemorrhage, blood transfusion, cesarean hysterectomy, intensive care unit admission, and death. Composite neonatal serious complications included shoulder dystocia with fetal injury (clavicular fracture, Erb palsy, Klumpke palsy, and hypoxic–ischemic encephalopathy), need for continuous positive airway pressure resuscitation or higher, NICU length of stay greater than 72 hours, sepsis, pneumonia, hypoxic–ischemic encephalopathy or periventricular leukomalacia, seizure, intracranial hemorrhage or periventricular hemorrhage, asphyxia, or neonatal death.
Indications for cesarean delivery were as recorded in the electronic medical record and mapped into predefined categories as previously described.5
The duration of the second stage of labor and rates of mode of birth (spontaneous vaginal, operative vaginal and cesarean delivery) as well as rates of composite maternal and composite neonatal outcomes for deliveries were calculated for each parity (nulliparous or multiparous) and epidural status (yes or no). Rates were plotted for each 0.5-hour interval duration of the second stage of labor on bar graphs. The denominator included deliveries occurring during each 0.5-hour interval.
For remaining analyses, we estimated a composite complication for maternal and neonatal complications combined. We first estimated for a given duration of the second stage of labor the additional probability that a woman would achieve a vaginal delivery and how often morbidity occurred during a subsequent time interval of 0.5 hours with additional duration of the second stage beyond a certain time point.
For analysis, we treated duration of the second stage of labor as a competing risk type of data. Competing risk events are said to be present when a patient is at risk of more than one mutually exclusive event such as death from different causes and the occurrence of one of these events will prevent any other event from ever happening. We considered the following three exclusive outcomes during the second stage of labor: 1) spontaneous vaginal delivery without maternal or neonatal serious morbidity or mortality, 2) birth by any mode with any maternal or neonatal serious morbidity or mortality, or 3) nonspontaneous vaginal delivery (ie, operative vaginal or cesarean delivery) without any maternal or neonatal serious morbidity or mortality. Note that, in our analysis, our main interest was in comparing the 1) spontaneous vaginal delivery with no morbidity against 2) deliveries with any morbidity, so we combined operative vaginal or cesarean delivery with no morbidity as one cause. This technique does not change our probabilities for the main objectives. For example, if one were interested in risk of cancer deaths against not dying from cancer, other causes of death would be combined. We estimated the probabilities of delivering by spontaneous vaginal birth without serious morbidity or mortality and probabilities of delivering by any mode with any serious morbidity or mortality during the subsequent 0.5-hour interval given that the woman had not delivered by the current time point based on a competing risk framework defined earlier. These probabilities are calculated as a ratio of the probability of a birth resulting from a specific cause occurring in the interval of interest with that of a probability of a woman at risk of delivering at the start of the time interval. These probabilities are based on cumulative incidence functions and overall survival probability (ie, probability of a woman still at risk for birth).6 Rates for additional intervals were also calculated.
Indications for cesarean delivery were calculated for extending the second stage of labor by 1 hour past historical definitions of second-stage duration for parity and epidural status.
All analyses were implemented using SAS 9.4 or R 3.1.2.
Nulliparous women incurred a serious maternal complication in 7.0% of cases with an epidural and 5.0% without an epidural; multiparous women incurred a serious maternal complication in 6.4% of cases with an epidural and 4.3% of cases without (Table 1). The neonatal composite serious outcome occurred in 4.3% and 3.2% of nulliparous and 2.7% and 2.2% of multiparous women with and without an epidural, respectively.
The empiric rates for mode of birth and maternal or neonatal morbidity or mortality for deliveries that occurred during each 0.5-hour interval of the second-stage duration are presented in Figure 1. Vaginal delivery rates were overall high, although decreased with increasing second-stage duration, a trend that was more variable for multiparous women. Neonatal morbidity or mortality rates increased and then leveled off for deliveries at greater than 4.0–4.5 hours for nulliparous women with an epidural. Each of the individual morbidity rates also tended to increase with increasing second-stage duration for nulliparous women without an epidural, indicating that the composite morbidity was not driven by any individual morbidity in particular (data not shown). Neonatal morbidity or mortality rates varied with increasing duration for nulliparous women without an epidural and for multiparous women.
We considered three exclusive outcomes during the second stage of labor. The percentages of women delivering by spontaneous vaginal birth without serious morbidity or mortality compared with the percentages of women delivering by any mode with any serious morbidity or mortality in the subsequent 0.5-hour interval among all the women who have not delivered at a given time point are presented in Table 2. Rates of spontaneous vaginal delivery without morbidity were slightly higher after the first half hour (greater than 0.5–1.0 hours) for nulliparous women, after which rates decreased with increasing second-stage duration. For multiparous women, rates of spontaneous vaginal birth without morbidity decreased with increasing second-stage duration. The rates of births with composite maternal or neonatal morbidity or mortality were variable with increasing second-stage duration but not inconsequential, ranging up to 5.6% for birth after greater than 4.0–4.5 hours of second-stage duration for nulliparous women with an epidural and 5.3% for birth after greater than 4.5–5.0 hours for nulliparous women without an epidural. For example, for nulliparous women with an epidural, given that a woman had not delivered in 3 hours, her likelihood of delivering with any serious morbidity or mortality in the subsequent half hour was 4.4% compared with her likelihood of delivering by spontaneous vaginal birth without serious morbidity or mortality, which was 19.5%. For multiparous women, the percentages of births with morbidity were more varied with the highest percentages in the first half hour of the second stage of labor (0–0.5 hours) and peaking again at 4.8% for birth after greater than 4.0–4.5 hours of second-stage duration for multiparous women with an epidural and 5.0% for birth after greater than 5.5–6.0 hours for multiparous women without an epidural.
Ranges of intervals are also provided in Table 3. For example, for nulliparous women with an epidural, given that a woman had not delivered in 3 hours, her likelihood of delivering with any serious morbidity or mortality in 1 hour beyond historic definitions of second-stage duration (greater than 3.0–4.0 hours) was 7.6% compared with her likelihood of delivering by spontaneous vaginal birth without serious morbidity or mortality, which was 31.4%. The rates for the previous hour (greater than 2.0–3.0 hours) were 6.9% and 37.5%, respectively.
Indications for cesarean delivery were calculated for extending the second stage of labor by 1 hour past historic definitions of second-stage duration for parity and epidural status (Table 4). The percentage of cesarean deliveries for nonreassuring fetal heart rate tracing for women without compared with women with an epidural were higher.
The rate of spontaneous vaginal delivery without morbidity was slightly higher after the first half hour (greater than 0.5–1.0 hours) for nulliparous women, after which rates decreased with increasing second-stage duration, whereas rates steadily declined for multiparous women. To assist in weighing the likelihood of vaginal delivery against the risk of serious maternal or neonatal morbidity or mortality, we provide data on both the risks and likelihood of spontaneous vaginal delivery without serious morbidity or mortality compared with the percentages of women delivering by any mode with any serious morbidity or mortality for increasing the duration of the second stage of labor.
Our findings are somewhat difficult to put into the context of the literature because modeling the outcomes of delivery and morbidity or mortality jointly in a competing risk framework in the same model is novel. In addition, many prior studies were limited in their ability to study rare serious morbidity and mortality given fewer numbers. The recommendations for the point at which to stop the second stage of labor have changed over recent years. Historically, maternal and neonatal risks have been considered to increase with a second stage beyond 2 hours and have been described with increasing duration in other studies.3,4,7–15 In an American College of Obstetricians and Gynecologists Practice Bulletin on operative vaginal birth from 2000, which was replaced in 2015 without mention of specific duration, operative vaginal delivery historically was considered an option in cases with lack of continuing progress for 2 hours without regional anesthesia in nulliparous women and 1 hour in multiparous women, with allowance for an additional hour with regional anesthesia.16 The American College of Obstetricians and Gynecologists and the Society for Maternal-Fetal Medicine have published an obstetric care consensus document acknowledging that although an absolute maximum duration of the second stage of labor is unknown, the diagnosis of second-stage arrest should not be made until at least 3 hours of pushing in nulliparous women and 2 hours of pushing in multiparous women and allowing consideration of longer durations in women making progress to be determined on an individual basis.17 These recommendations note the importance of progress with pushing, which is distinct from whether active compared with a passive second stage of labor may be associated with differences in maternal and neonatal outcomes and requires future study. In our study, we did not observe an inflection at a particular hour mark. The percentage of women having a spontaneous vaginal birth without serious maternal or neonatal morbidity steadily decreased regardless of parity or epidural status for increasing second-stage duration (except for the first half hour for nulliparous women), whereas the percentage of deliveries by any mode with serious morbidity was variable but not inconsequential. Ultimately the willingness to accept a certain percentage risk of morbidity to achieve vaginal delivery is up to the woman and clinician.
The major strength of our study is the large numbers and multiple centers allowing investigation of rare serious morbidity and mortality. However, our study is limited by the retrospective nature of the data. The decision-making for women who were allowed to have longer second-stage durations likely was complex and may have included a number of factors such as progression, maternal and neonatal status, clinician experience, and the clinician–patient relationship. It is unclear how the interplay of these factors could have influenced the success of vaginal delivery and rate of adverse outcomes. In addition, we did not have information on active compared with delayed pushing. The generalizability of our findings might be slightly less given the increasing obesity in the United States since the original data collection. Data on long-term maternal morbidity including incontinence and child neurologic outcomes are also lacking.
Data to assist in decision-making for extending the second stage of labor beyond the historical definitions of second-stage duration are limited. Additional factors such as progress in descent, station achieved, position of the head, estimated fetal weight, maternal fatigue, the presence of chorioamnionitis or meconium, and fetal heart tracing are important to take into account when deciding on the length of the second stage of labor for any individual patient. Although we cannot make a recommendation for the optimal second-stage duration, our findings will assist clinicians and patients in the decision for weighing the likelihood of spontaneous vaginal delivery with the risk of serious maternal and neonatal morbidity or mortality when considering continuing the duration of the second stage of labor.
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